1. Field of the Invention
This invention relates to a method of improved phosphate rcovery in a flotation of phosphate ore and more particularly to the recovery of phosphate from the froth product tailings which are now considered waste product of a conventional flotation process.
2. Description of the Prior Art
Various types of methods have been devised by the prior art for processing raw phosphate ore into phosphate by-products including phosphoric acid, superphosphoric acid, fertilizers and the like. The various processes have been adapted in accordance with the type of phosphate ore present in various parts of the world and in accordance with the amount of phosphate contained in the ore matrix. Different grade matrix ores required different processes for extracting the phosphate from the ore in the most economical way.
The double flotation process is commercially used for the beneficiation of phosphate ore when the phosphate ore matrix contains impurities such as silicate materials. In this process, the beneficiation of phosphate ore begins by digging the ore matrix from the ground. The ore matrix is used to form a slurry with water and pumped to a beneficiation plant. The coarse phosphate rock is screened out on a screen size generally -20 mesh. Material passing through the -20 mesh screen is deslimed at 150 mesh. The material passing through the 150 mesh is called "slimes" and contains mostly clay, silica and phosphate. The slime is typically discarded in the conventional double flotation process. The usable ore typically (-20 to +150 mesh) is passed through a first flotation process for extracting the phosphate from the deslimed matrix. The usable ore is treated with a fatty acid fuel-oil (an anionic agent) conditioned in an alkali solution which causes the desired phosphate ore to float upon an underfloat. The underflow, generally called "rougher tailings" is discarded in the conventional flotation process. The desired phosphate ore or overfloat, typically called "rougher concentrate" is deoiled with sulphuric acid to remove the anionic reagent and is then washed with water. Thereafter, the washed overfloat is treated with an amine and kerosene (cationic reagent) in a second flotation process. The second flotation process removes silica which floated during the first flotation process generally called "froth product tailings" to produce a final concentrate grade of 70-76 percent BPL (boned phosphate of lime) which is the desired product from the flotation process. The forth product tailings which are separated in the second stage from the final concentrate grade of phosphate is discarded under most prior art flotation processes. This froth product tailing contains from 8%-25% BPL, but have been considered waste and discarded since there has not been an efficient and inexpensive method of extracting the 8%-25% BPL from the froth product tailing.
Arthur Crago disclosed in U.S. Pat. No. 2,293,640, a method of concentrating phosphate materials from ore which comprises, in the first step, subjecting the ore to an aqueous pulp to a concentrating operation with negative ion reagents to separate a rougher concentrate of the phosphate ore and entrained silicious gangue. The second step of the Crago process involved treating the rougher phosphate concentrate with a mineral acid to neutralize the negative ion reagent used in the production of the rougher concentrate. The third step of the Crago process included subjecting the acid treated rougher phosphate concentrate with a positive ion reagent. The positive ion reagent is a selective collector for the gangue which is material largely composed of silicious gangue thereby producting the final phosphate concentrate.
A further improvement of the Crago process was disclosed by James D. Duke et al in U.S. Pat. No. 2,753,996. Duke et al improved upon the Crago method since Duke recognized a substantial loss of phosphate ore in the silicious froth product since in practice it is impossible to produce pure silica float. In the concentration of phosphate material by flotation employing only negative ion reagents, the middling product from the cleansing operation is often returned and passed through the process again with a new phosphate ore. However, the silicious froth product cannot be treated as a middling in that way. In attempting to follow such a procedure in practicing the Crago method, a considerable amount of silica floats with the rougher concentrate thus lowering the grade of the finished phosphate concentrate. In addition, some of the phosphate does not float thus causing a loss of phosphate in the tailings and the accumulation of phosphate in the middling which is returned to the original feed. In the practice of the Crago method, the silicious froth product containing a large amount of the silica which was removed from the rougher flotation product was discarded along with a considerable amount of phosphate.
Accordingly, Duke proposed the treatment of the silicious froth product with positive ion reagents as a middling in a manner which permits the recovery of a larger part of the phosphate which was heretofore discarded.
In the Duke process, the silicious frother product is agitated in an aqueous pulp with a colloidal clay such as bentonite, phosphatic clay, kaolin or Fuller's earth. Duke further proposed that the step of agitating the silicious middling with a colloidal clay took place before returning the middlings to the new feed and that the middlings be added to the new feed after the new feed had been conditioned with the necessary negative ion reagent.
The Duke process proposed a novel concept for the improved recovery of the concentration of phosphate materials, but unfortunately systems utilizing this method experienced substantial build-up of the silicious materials within the flotation process which substantially lowers the final grade of phosphate concentrate or lowers the efficiency of the separation in the first and second flotation processes.
Therefore, it is an object of this invention to provide a method for improving the recovery in a conventional phosphate ore flotation process which recovers at least a portion of the phosphate in the froth product tailing without the build-up of silicious material within the primary flotation process.
Another object of this invention is to provide a method for improving the recovery in a conventional phosphate ore flotation process which utilizes a discarded by-product as an activating agent for the recycling of the froth product tailings.
Another object of this invention is to provide a method for improving the recovery in a conventional phosphate ore flotation process which will produce both high grade phosphate ore and an improved recovery without the undesired build-up of silicious material within the flotation process.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.